An ant‐mimicking ant on an oceanic archipelago: Camponotus guanchus mimics Crematogaster alluaudi—An analogy with the situation of Camponotus lateralis (Hymenoptera: Formicidae)

Abstract Mimicry, that is, the imitation of any unpalatable or defensive species by another, has been of central interest to evolutionary research since Darwin's lifetime. Two ant species, Camponotus guanchus Santschi, 1908 and Crematogaster alluaudi Emery, 1893, endemic to the Canary Islands, occur in two color‐morphs: While the head of workers is always reddish and the gaster blackish, the mesosoma (inclusive waist) is either fully reddish or fully blackish. In addition to the obvious morphological and coloration similarities, we provide evidence of mimicry: (i) Ca. guanchus was found only within the area of Cr. alluaudi. (ii) Color morphs are geographically non‐randomly distributed: Workers of both species from 16 localities of syntopic occurrences shared in eight cases a blackish and in eight cases a reddish mesosoma. Hence, Ca. guanchus mimics both local color‐morphs of Cr. alluaudi. We consider a fascinating analogy with the Mediterranean mimicry system in Camponotus lateralis (Olivier, 1792) and its model species of the Crematogaster scutellaris (Olivier, 1792) group on an island scale. Additionally, we present two endemic bug species, Perenotus stysi (Ribes et al., 2008) and P. malobae Roca‐Cusachs & Goula, 2016, as mimics of those Cr. alluaudi workers having a reddish mesosoma. Our distribution, coloration, frequency, and behavioral data as well as the analogy with Ca. lateralis and the Cr. scutellaris group suggest a Batesian‐mimicry system in which Ca. guanchus, Perenotus stysi, and P. malobae mimic the unpalatable and aggressive Cr. alluaudi as an antipredator adaptation.


| INTRODUC TI ON
Shortly after Charles Darwin postulated the theory of natural selection (Darwin, 1859), Henry W. Bates described Batesian mimicry in Lepidoptera.He found that species with obvious similarities in color were not always closely related.Most Lepidopteran species with striking colors were toxic and thus unpalatable for insectivores (aposematism sensu Poulton, 1890).Some palatable species mimicked the color of toxic species as an antipredator adaptation (Bates, 1861).From that time on, mimicry has remained a topic of central interest for evolutionary research (Darwin, 1871;Fisher, 1930;Komárek, 2002;Quicke, 2017;Ruxton et al., 2004;The Heliconius Genome Consortium, 2012;Wallace, 1866;Wickler, 1968).In Batesian mimicry, the morphology and color of mimics resembles that of any unpalatable or defensive species (i.e., the model); mimics enjoy reduced predation without the need to evolve a costly defense like a toxin or sting (Franks & Noble, 2004;Wickler, 1968).
The Canary Islands are an archipelago of volcanic origin, formed by seven main islands about 90 km off the northwest coast of the African continent.With an area of 7492 km 2 , the Canary Islands have 7820 invertebrate species (45% endemics), of which 61 are ant species (31% endemics) (Gobierno de Canarias, 2024).In general, the origin and distance from the continent have turned oceanic islands into "laboratories" for the study and understanding of evolutionary processes (Gillespie & Roderick, 2002;Graham et al., 2017;Whittaker & Fernandez-Palacios, 2007).The biota of these islands are characterized by: (i) having fewer species per area unit than those on the continent, (ii) having a different balance of species compared to areas with an equivalent size on the continent (island disharmony), and (iii) a high number of endemic species (Whittaker & Fernandez-Palacios, 2007).
Camponotus guanchus (Formicinae) was known to occur on the islands of El Hierro, La Palma, and Tenerife to date (Gobierno de Canarias, 2024), in this publication we provide data also for the island La Gomera (Table A1 in Appendix).This species has two color variants, which we call "color morphs."While the head of both morphs is reddish and the gaster blackish, the mesosoma (including the waist) is either entirely reddish (reddish morph) or entirely blackish (blackish morph) (Figure 1).Following the current taxonomic status, both color morphs belong to the same species (Cagniant & Espadaler, 1993).Camponotus guanchus was described from the north of Tenerife (Santschi, 1908) and the holotype has a blackish mesosoma (see AntWeb, CASENT0911695).We are not the first to have noticed the similarity between Ca. guanchus and Cr.alluaudi: Santschi (1919) mentioned color mimicry in Ca. guanchus and Emery (1893) compared the relationship between Ca. guanchus and Cr.alluaudi with that between Ca. lateralis (Olivier, 1792) and Cr.scutellaris (Olivier, 1791) in the Mediterranean.However, these authors only reported about the blackish morphs.Camponotus guanchus might be very closely related to Ca. ruber Emery, 1925, a taxon occurring in North Africa and South Europe (Cagniant, 1996;Schifani et al., 2022;Seifert, 2019).Although the unique petiole shape in Ca. guanchus workers makes a putative synonymy with this taxon unlikely (Cagniant & Espadaler, 1993), the possibility of a synonymy should be proven by a modern taxonomic-revision including morphometric or nuclear molecular-genetic data.
Crematogaster alluaudi (Myrmicinae) is suggested to be the model species of this mimicry system.It is territorial and very aggressive (personal observations).Workers, if alerted, fold their gaster up above the mesosoma in a scorpion-like manner (Barquín Diez, 1981).All Crematogaster species secrete a defensive venom, produced by the Dufour's gland, when disturbed (Buren, 1959;Daloze et al., 1987Daloze et al., , 1991)).This venom can kill other ants rapidly (Marlier et al., 2004;Seifert, 2018) and possibly makes them unpalatable to vertebrate predators (Emery, 1886;Ito et al., 2004;Wagner, 2013Wagner, , 2014)).Crematogaster alluaudi is distributed over four of seven islands of the archipelago: El Hierro, La Palma, La Gomera, and Tenerife (Gobierno de Canarias, 2024;Table A1 in Appendix).This species appears in the same two color-morphs as Ca.guanchus (Figure 1).Its subspecies Cr. alluaudi noualhieri Emery, 1893 is restricted to the northern slope of the island Tenerife.Its blackish mesosoma-color is the only distinct difference from the nominate form (Santschi, 1937).The evaluation of putative small morphological differences (Barquín Diez, 1981;Emery, 1893) would require morphometric data.Since the status as subspecies is taxonomically doubtful, we use here the term "color morph".
Analogous to the situation in Ca. guanchus and Cr.alluaudi, also the Mediterranean ant Ca. lateralis (Olivier, 1792) and its Crematogaster model species have regional mesosoma-color differences.In some regions, for example, over large parts of the Balkans, Ca. lateralis has a reddish mesosoma like Crematogaster schmidti (Mayr, 1853).In other regions, for example, over large parts of Italy, it has a blackish one like Cr. scutellaris (Olivier, 1791).It has already been hypothesized that the submissive (Borovsky et al., 2022;Marlier et al., 2004;Menzel et al., 2010) Ca. lateralis mimics the color of the regional occurring dominant and very aggressive Crematogaster model species (Seifert, 2018(Seifert, , 2019;;Wagner, 2013Wagner, , 2014)).
This study aims to demonstrate evidence of mimicry of Ca. guanchus beyond the obvious resemblance to Cr. alluaudi.For this purpose, we analyzed the geographic distribution of Ca. guanchus and Cr.alluaudi and their putative mesosoma-color coincidence in sympatric occurrences.We hypothesize that the two color-morphs of Ca. guanchus mimic the local color-morphs of Cr. alluaudi.The alternative hypothesis is that there is no mimicry between these species.This option would be valid if the distribution of Ca. guanchus (and its color morphs) was not linked to the distribution of Cr. alluaudi (and its color morphs) but distribution as well as the matching of colormorphs was random.We expect Perenotus to occur only in regions where Cr. alluaudi workers share its reddish mesosoma.

| MATERIAL S AND ME THODS
Distribution data of Ca. guanchus, Cr. alluaudi, and Perenotus spp.
were obtained from the collection of Antonio J. Pérez-Delgado and the citizen-science platform iNaturalist (https:// www.inatu ralist.org/ ), the material was collected between 2001 and 2023 (Table A2 in Appendix).All available Ca. guanchus, Cr. alluaudi, and Perenotus spp.records were considered for distribution maps (QGIS Development Team, 2019) but the statistical analysis was performed with the information from the database only (IBM SPSS Statistics 19).Perenotus records were not tested statistically due to their low number.The behavior of ants was observed directly in the field.
To test if Ca. guanchus follows the island distribution of Cr. alluaudi rather than those of other Canarian ant-taxa (which were predicted to be outside of the mimicry system), island distribution of Ca. guanchus, Cr. alluaudi, and all other Canarian ant-taxa were listed (Table A1 in  To evaluate the putative geographic coincidence of mesosoma colors between the two species, a matrix including the cases in which both species were in syntopy was established (Table 1).
Fisher's exact test (Fisher, 1922(Fisher, , 1925)), a conservative statistical method (Crans & Shuster, 2008), was used to test how probable the common occurrences of the same color-morphs of both species were a random result.The one-tailed p-value was accepted.An αlevel of .05 was used.
Images of the habitus were taken using a Canon EOS 750D attached to a Zeiss Stemi 2000 stereomicroscope, multiple images were processed with Zerene Stacker (V.1.04,Zerene Systems, LLC., Richland, USA) to generate an improved single image using pmax and dmap methods.Additionally, more specimens were photographed in their habitat using a NIKON D5100 and objective Sigma 105 mm.

| RE SULTS
From 930 localities throughout the Canary archipelago included in the collection of Pérez-Delgado, Ca. guanchus and Cr.alluaudi were found at 90; we added also 39 records from iNaturalist (https:// www.inatu ralist.org/ ) to get a total of 129 records from the islands El Hierro, La Palma, La Gomera, and Tenerife.Ten records of Perenotus on the islands Tenerife and La Palma were known (see Figure A3 in Appendix).
Of 59 Canarian ant-taxa outside the mimicry system, 33 were native to the Canary Islands (see Table A1 in Appendix) (Gobierno de Canarias, 2024).Based on our presence list of ants of the seven Canary Islands (Table A1 in Appendix), only one taxon (3.0%) resembles the island distribution of Cr. alluaudi and Ca.guanchus: Temnothorax gracilicornis (Emery, 1882) is the only native species outside the mimicry system which occurred also only on the four western but not on the three eastern islands.
All observed workers had either an entirely reddish or blackish mesosoma (Figure 1), no worker with intermediate coloration was found.No intracolonial coexistence of the two color-morphs was detected either.The reddish color-morphs were found on all four islands, those with a blackish mesosoma only on the northern slope of Tenerife (Figure 2; Figure A3 and Table A2 in Appendix).Tenerife is the only island from where both color-morphs of both species were recorded.The distribution areas of color morphs of Ca. guanchus were within those of the equivalent color morph of Cr. alluaudi (Figure 2).A single worker of the reddish color-morph of Ca. guanchus (cod.3052_TF-345) broke this rule (Figure 2a).In our study, at 99 sample points Cr. alluaudi (any color morph) was found and at 16 of them also Ca. guanchus was detected.In eight of these cases, both species had a blackish and in further eight cases a reddish mesosoma (for details see Table A2 in Appendix).No locality with a mesosomacolor difference between Ca. guanchus and Cr.alluaudi was detected (Table 1).The probability for the described color-pattern between the two species to be a random result is p = .0001.When both species occurred syntopically, Ca. guanchus was always in the minority and did not exceed 10% of individuals of Cr. alluaudi workers.The workers of both species were commonly observed foraging on the same plant.We observed three times weakly-used mixed trails of both species leading to flowers of Euphorbia lamarckii; workers of Including literature data, there are 10 localities where the genus Perenotus was detected so far (Ribes et al., 2008;Roca-Cusachs & Goula, 2016).We found one individual within a nest of Cr. alluaudi.
All individuals shared the distribution as well as the color pattern (Figures A2 and A3 in Appendix) with Cr. alluaudi workers having a reddish mesosoma (Figure A2 in Appendix).From localities in the north of Tenerife, where workers of Cr. alluaudi had a blackish mesosoma, no Perenotus records were made.

| DISCUSS ION
We demonstrated the hypothesis of mimicry between Ca. guanchus and Cr.alluaudi based on the following findings:

| Sympatric occurrence
The species Ca. guanchus and Cr.alluaudi were both found only on the four western islands (El Hierro, La Palma, La Gomera, and Tenerife).
The fact that this horizontal distribution-pattern in the archipelago is shared with only one single ant-species outside the mimicry system (Temnothorax gracilicornis) indicates a rare occurrence.Among our target species, Cr. alluaudi has a wide vertical distribution ranging from coastal to high mountain habitats, the most frequent habitat is thermo-sclerophyllous woodland.Camponotus guanchus has a narrower niche, often limited to thermo-sclerophyllous woodland, Euphorbia scrub, and shrublands (del Arco Aguilar & Delgado, 2018; 93% of observations).Therefore, we consider the horizontal and vertical distribution of Ca. guanchus to be fully within that of Cr. alluaudi (Figure 2; Figure A3 and Table A2 in Appendix).

| Same color morphs occur syntopically
While the morphs with the reddish mesosoma of both species occurred on all four islands, we found workers with a blackish mesosoma in both species only on Tenerife.Our results show that the color morphs of both species were geographically segregated: The blackish morph of both species occurred on the northern slope of the island and the reddish morph on the rest of the island (Figure 2).
The results allowed us to detect contact zones in which the different color-morphs were close together (Figure 2; Table A2 in Appendix).
We have detected only one outlier contradicting the spatial structure of the color morphs: One specimen of Ca. guanchus with a reddish mesosoma was detected within the area of the blackish color-morph (Figure 2a; Table A2 in Appendix).Since this specimen was found in an anthropized area of vegetal-waste deposit, there is a possibility that it was introduced.
The results show that, when both species were in syntopy, their mesosoma colorations were not random.We found a significant local congruence between the mesosoma colors of Ca. guanchus and Cr. alluaudi when we analyzed the results at the archipelago level.
If we focused on the island Tenerife, we have found the species in syntopy nine times and in 100% of cases the color morph of the mimic coincided with that of the model.Due to the low number of samples on island level, we have not been able to do statistical analyses but still the mimicry seems obvious.Since we have not detected intermediate-colored workers or colonies with both color-morphs in Cr. alluaudi as well as Ca.guanchus, we believe that inter-color mating is not common.Color coincidence is a key fact that confirms our hypothesis of mimicry.This result makes us believe that Ca. guanchus, fascinatingly, represents a mimic with a similar evolutionary history as the not very closely related (Seifert, 2019) species Ca. lateralis: Local color-morphs are hypothesized to occur in dependence on the color of Crematogaster models (Seifert, 2018(Seifert, , 2019;;Wagner, 2013Wagner, , 2014)).
While the mimicry system of Ca. lateralis extends over an area of more than 1,000,000 km 2 (Mediterranean, Black Sea Region, Anatolia, and Caucasus), the mimicry system of Ca. guanchus extends over an insular area of only ca.3300 km 2 .In the Ca.lateralis mimicry-system, there are three very closely related (Blaimer, 2012) model species (Cr. scutellaris, Cr. schmidti, Cr. ionia Forel, 1911), which also hybridize at least partly (Bračko, 2023;Seifert, 2018), but only one mimic species (Ca.lateralis) (Seifert, 2019).In contrast, the mimicry system on the Canary Islands includes probably a single model-species, Cr. alluaudi, with two color morphs.Moreover, Ca. ruber, a further Mediterranean taxon very similar in color and morphology to Ca. guanchus and putatively closely related (if not conspecific), has also been suggested to be a mimic of Cr. scutellaris (Schifani et al., 2022) parts of Europe has driven their color mimicry and thus their speciation process (Schifani et al., 2022).It seems possible that intraspecific color-morphs of Ca. guanchus or Ca.lateralis are at an earlier evolutionary stage of speciation than the two Colobopsis species.
Analogously, we observed workers of Ca. guanchus in shared trails escaping when they encountered a Cr.alluaudi worker.Due to the low abundance of Ca. guanchus, unfortunately, we made only few observations and definite observation sets lack.
The genus Perenotus is a further member of the proposed mimicry system.Its morphology, coloration, and distribution coincide with that of the reddish morph of Cr. alluaudi.Furthermore, the presence of one individual of P. malobae inside a nest of Cr. alluaudi underpins the mimicry hypothesis.All these findings raise questions concerning the putative unpalatability of Cr. alluaudi for predators.
One could suspect whether such a tiny number of potential vertebrate predator taxa is sufficient to drive the evolution of aposematism and mimicry.However, a high average density of individuals (density compensation) compensates this low vertebrate species richness of insular ecosystems (Whittaker & Fernandez-Palacios, 2007).Density compensation refers to a higher-thannormal density related to empty-niche phenomena and reduced predation (Novosolov & Meiri, 2013;Whittaker & Fernandez-Palacios, 2007).Several studies have estimated maximal densities of Gallotia galloti on Tenerife at 1300-3300 individuals/ha (De Los Santos & De Nicolás, 2008;Farina & Aguilar, 2002).To summarize a conclusion, we interpret predation pressure by Gallotia lizards to be high enough to drive of evolution in the proposed mimicry-system.This interpretation, however, presumes that Gallotia should avoid the model of the mimicry system, most likely Cr. alluaudi.

| Is the mimicry of Ca. guanchus Batesian?
It is believed that predation pressure drives the evolution of aposematism (Poulton, 1890;Quicke, 2017;Wickler, 1968).By means of aposematism, Cr. alluaudi might defend itself against sympatric predators which perceive reddish color.The color pattern would be particularly suitable for an optical differentiation from other ants.Nowadays, the classical categorization (Wickler, 1968) into Batesian (Bates, 1861) versus Muellerian (Müller, 1879) mimicry is considered to represent a simplification (Speed, 1999).Instead, there is a mimetic spectrum of species that vary in their honesty and their degree of unpalatability or defensiveness between the lower and upper extreme, that is, Batesian and Muellerian mimicry (Pekár et al., 2017).We argue that Ca. guanchus might be close to the lower extreme of this spectrum, that is, in the classical sense (Wickler, 1968), Batesian mimicry.The alternative hypothesis would be that predators do not have a preference for Ca.guanchus or Cr.alluaudi, and instead are repelled by both (e.g., the formic acid of Ca. guanchus and the venom of Cr. alluaudi).If this alternative hypothesis was true, the color signals would represent Muellerian mimicry (Müller, 1879;Wilson et al., 2015).In the following, we present arguments for an allocation of Ca. guanchus within the classic concept of Batesian and Müllerian mimicry: 1.In syntopic occurrence, the frequency of Ca. guanchus workers did not exceed 10% of that of Cr. alluaudi.Being in the minority compared to individuals of the model is typical for Batesian but not for Muellerian mimics (Kikuchi & Pfennig, 2010;Wickler, 1968).
2. The distribution area of Ca. guanchus is embedded within those of Cr. alluaudi while the latter has a wider ecological niche (Figure 2; Figure A3 and Table A2 in Appendix).This finding is in line with most other cases of Batesian ant-mimicking ants, where models had a larger area than their mimics (Gallego Ropero & Feitosa, 2014;Ito et al., 2004;Merrill & Elgar, 2000;Schifani et al., 2022); theoretically, Batesian mimics are expected to co-occur with their models (Kunte et al., 2021;Pfennig & Mullen, 2010).
3. Workers of Ca. guanchus follow trails of Cr. alluaudi and, consequently, seek their physical closeness (which should be adaptive for a Batesian mimic).Vice versa, Cr. alluaudi behaves aggressively to Ca. guanchus, which should be adaptive for a model to avoid physical closeness to a mimic weakening the honesty of the aposematic signal (Kikuchi & Pfennig, 2013).
4. In the analogous mimicry system in the Mediterranean, represented by Ca. lateralis and the Cr.scutellaris group, it was shown that Italian wall lizards (Podarcis sicula) ingest highly significant more Ca.lateralis group workers than those of the Cr.scutellaris group (Wagner, 2013(Wagner, , 2014;;H. C. Wagner et al., in prep.).We expect that the defense chemicals of ants in the here described Canarian mimicry-system are similar.More generally, even if ant acid of Camponotus might be unpalatable for some predators, formicine ants may be relatively more vulnerable to predation than those of other subfamilies (Lamon & Topoff, 1981;Merrill & Elgar, 2000;Montgomery, 1985;Seifert, 2009).
Appendix) based on literature information (Gobierno de Canarias, 2024) and own collecting activity.The percentage of native ant-species outside the mimicry system sharing the island distribution of Cr. alluaudi is considered as p-value to estimate how probable the shared island-distribution of Ca. guanchus and Cr.alluaudi is a random result.F I G U R E 1 Workers of Camponotus guanchus and Crematogaster alluaudi with different mesosoma colors.(a) Ca. guanchus and (b) Cr. alluaudi workers with a reddish mesosoma collected on La Palma, Monte de Luna, 02/03/2021; (c) Ca. guanchus and (d) Cr. alluaudi noualhieri workers with a blackish mesosoma collected on Tenerife, Punta del Hidalgo, 17/07/2021.Individuals deposited in the A. J. Pérez-Delgado collection.

F
Ca. guanchus escaped when they encountered a Crematogaster worker.Two times Cr.alluaudi workers were present at the flowers and Ca.guanchus workers kept distance.TA B L E 1 Syntopic occurrences of color-morphs of Ca. guanchus and Cr.alluaudi on the Canary Islands.I G U R E 2 Distribution of color morphs of Camponotus guanchus and Crematogaster alluaudi on the island Tenerife.The circles correspond to Cr. alluaudi and the triangles Ca. guanchus.(a) Reddish color-morphs and (b) blackish color-morphs of both species.
Camponotus guanchus worker (a) and Crematogaster alluaudi worker (b).Detail of the head, dorsal view, and lateral view of both species.The scale is equivalent to 1 mm.F I G U R E A 2 Habitus of Perenotus malobae-a myrmecomorphic Heteroptera species mimicking Crematogaster alluaudi in color and morphology.Specimen collected at Monte de Luna, La Palma.Individual deposited in the Pérez-Delgado collection.F I G U R E A 3 Distribution of the mimicry-system members on Canary Islands: Crematogaster alluaudi (circles), Camponotus guanchus (triangles), Perenotus malobae (black crosses), and Perenotus stysi (purple crosses).
Known distribution of Camponotus guanchus and Crematogaster alluaudi based on data of the collection (col) of Pérez-Delgado and iNaturalist.
TA B L E A 2